Logical Data Structure

EMarketOffer uses two broad types of data:

Static Data: Static data describes the Items Modelled in EMarketOffer (e.g. Generator maximum capacity).

Dynamic Data: Dynamic data described the state of the Modelled Items defined by the static data and changes rapidly over time, typically by Trading Period (e.g. Nodal Price)

Terminology

EMarketOffer's data design consists of 'things' included in the model, and the characteristics of those 'things'. In this manual the 'things' are called Entities and their characteristics are called Traits. Traits may be static or dynamic.

For example the Circuit Entity can have the static Traits of Start Node and End Node, and the dynamic Traits of Powerflow and Loss by Trading Period.

---

NOTE: : Static data is not permanently fixed and may, at times, be quite changeable, but within the context of EMarketOffer it is not necessary to be able to track such changes down to the Trading Period level.

---

Modelled Items

Four broad categories of item (Entity) are modelled in EMarketOffer:

Item Type	Relate To
System	The physical Transmission System
Market	The routine operation of the wholesale Market (Offers, Load, Price)
Commercial	Generation Companies and their retail and hedging operations
Geographical	Physical points and regional positioning

System Items

The following table lists and describes the System items modelled in EMarketOffer.

Item (Entity)	Description	Attribute (Trait)
System Node	Any point in the NZ Transmission System to which a Circuit can be connected	Name
Substation	One or more System and/or Market Nodes located at a single geographical location	Name Component Node
Circuit	A branch (Circuit) conducting power on the NZ Transmission System	Name From Node To Node Contributes to HVDC (Yes/No) Resistance Reactance Capacity (Summer/Winter)
Branch Constraint	A Transpower defined Constraint affecting a single Circuit	Name Circuit Start Date and Period End Date and Period Value
Equation Constraint	A Transpower defined Constraint affecting more than one circuit	Name Start Date and Period End Date and Period Affected circuits Constraint Equation Limit (RHS)
Reserve Region	A Transpower defined Region used for calculating	Reserve Region Name

Market Items

The following table lists and describes the Market items modelled in EMarketOffer

Item (Entity)	Description	Attribute (Trait)
Market Node	A system Node at which electricity can be injected or withdrawn and for which a Nodal Price is published in the NZEM	Name (System Node)
Unit	A single physical electricity generation Unit for which Offers can be made	Name Connection (Market Node)
Generator	A logical collection of (typically geographically co-located) Units	Name Component Units

Commercial Items

The following table lists and describes the Commercial items modeled in EMarketOffer

Item (entity)	Description	Attribute (trait)
Company	An owner of Generation capacity	Name Unit(s) Unit Name Cost ($/MWh) Retail Node(s) Node Name Percentage load owned Retail price ($/MWh) Hedge Contract(s) Reference Node name Hedge start date Hedge start period Hedge end date Hedge end period Price ($/MWh) Quantity (MW)

Geographical Items

The following table lists and describes the Geographical items modelled in EMarketOffer

Item (entity)	Description	Attribute (trait)
Region	A logical collection of Substations (typically but not necessarily geographically co-located)	Name Component System nodes

Note: The Items listed above are not all modelled at the same level in EMarketOffer. For example no distinction is made in the program between System and Market Nodes with Prices being calculated for all System Nodes in Forecasts. Also Branch Constraints are treated as complex attributes of individual circuits rather than Items in their own right.

Dynamic Data

Dynamic data Traits that changes value frequently, typically by Trading Period. The following table lists the dynamic data items modelled in the EMarketOffer:

Modelled Item	Attribute	Units	Comment
rowspan="5" Circuit